An electric actuator includes a feed screw shaft that rotates by operation of a motor, and a nut that is screw-engaged with the feed screw shaft. As this feed screw shaft, in general, a ball screw shaft or a sliding screw shaft is used. In view of abrasion resistance, the ball screw shaft is made of quenched steel and the sliding screw shaft is made of iron, and nickel-plated or hard-chromium-plated. The nut screw-engaged with the sliding screw shaft is made of copper, resin, etc.
For example, Japanese Laid-Open Patent Publication No. 2014-047884 proposes a technical concept regarding an electric actuator having a ball screw shaft. In the actuator, a diamond-like carbon (DLC: Diamond-Like Carbon) film is formed on a rod seal member to decrease the friction coefficient between the rod and the rod seal member to ensure smooth operation, and improve abrasion resistance.